They don’t call it the boob tube for nothing: TV viewing time is correlated with changes in the brain, according to a Japanese study of children between the ages of five and 18. The more kids watch, the more gray matter builds up at the front of the frontal lobe. That’s brain flab, wrote researchers in Cerebral Cortex. It’s linked to lower verbal intelligence.

However, it’s not clear that watching TV caused the changes. Heavy TV viewing may crowd out other activities, such as playing, reading or talking with friends and family. Perhaps not-so-bright kids are more likely to become TV addicts.

As schools ratchet up academic standards for all students, new buzzwords are “persistence,” “risk-taking” and “resilience” — each implying more sweat and strain than fuzzy, warm feelings.

“We used to think we could hand children self-esteem on a platter,” Stanford University psychologist Carol Dweck said. “That has backfired.”

. . . children praised for trying hard or taking risks tend to enjoy challenges and find greater success. Children also perform better in the long term when they believe that their intellect is not a birthright but something that grows and develops as they learn new things.

Brain imaging shows “connections between nerve cells in the cortex multiply and grow stronger as people learn and practice new skills.” Montgomery County (Maryland) schools now teach children that they’re developing their brains when they struggle to learn something new. Teachers also try to provide specific feedback on how students can improve instead of a vague “Good job!”

Praise should be used to encourage students to take risks and learn from failure, Dweck said. “Does the teacher say: ‘Who’s having a fantastic struggle? Show me your struggle.’ That is something that should be rewarded.”

Delay Kindergarten at Your Child’s Peril, warn neuroscientists Sam Wang and Sandra Aamodt, authors of Welcome to Your Child’s Brain: How the Mind Grows From Conception to College, in the New York Times.

Nine percent of children old enough to start kindergarten are “redshirted” each year by parents who want to give them an edge, they write. But the advantages usually fade by the end of elementary school. “In high school, redshirted children are less motivated and perform less well.”

In a large-scale study at 26 Canadian elementary schools, first graders who were young for their year made considerably more progress in reading and math than kindergartners who were old for their year (but just two months younger). In another large study, the youngest fifth-graders scored a little lower than their classmates, but five points higher in verbal I.Q., on average, than fourth-graders of the same age. In other words, school makes children smarter.

High achievers benefit from skipping a grade, they add. Acceleration has twice the effect on achievement as programs for the gifted.

Children do best when they’re challenged, but not overwhelmed.

Learning is maximized not by getting all the answers right, but by making errors and correcting them quickly. In this respect, children benefit from being close to the limits of their ability. Too low an error rate becomes boring, while too high an error rate is unrewarding. A delay in school entry may therefore still be justified if children are very far behind their peers, leaving a gap too broad for school to allow effective learning.

Young children’s brains are developing rapidly. For most, the best possible contest is the classroom, Wang and Aamodt believe. That’s especially true for disadvantaged children. The trend to move back the cutoff date for starting kindergarten is hurting children from low-income families, they write.

My husband skipped a grade in elementary school. My sister skipped in middle school. Neither faced much of an error rate in the higher grade. My daughter’s half-sister skipped high school, starting college at 14. It was not an academic challenge. Now 18, she’s started graduate school in classics.